1. Field of the Invention
The present invention relates to a method for estimating deceleration of a wheeled vehicle during a transmission gear shift.
2. Background Art
Wheeled vehicles, such as automobiles and trucks, have transmissions that adapt the power of an engine to meet varying road and load conditions. Such transmissions may have an input shaft connected to an engine and an output shaft adapted to drive vehicle traction wheels. The torque provided to the vehicle traction wheels by the output shaft is interrupted during a transmission gear shift. As a result, the speed of the vehicle may decrease during the gear shift.
Shift control systems, such as that disclosed in U.S. Pat. No. 5,272,939, use an engine torque value and a vehicle acceleration value to predict whether a shift is feasible before commencing a gear shift. These inputs must be heavily filtered or dampened to reduce noise due to vehicle driveline dynamics, such as the torsional vibrations. This filtering causes the filtered signals to lag real time signals and can result in late transmission gear shifts. In addition, the vehicle acceleration value is obtained by differentiating a shaft rotational velocity signal. Differentiating the rotational velocity signal increases the signal noise by a significant order of magnitude and may lead to suboptimal shift decisions that reduce fuel economy and degrade transmission performance.
According to the present invention, a method for estimating deceleration of a vehicle during a transmission gear shift is provided. The method includes the steps of determining an expected vehicle deceleration during a transmission gear ratio shift to a target gear ratio as a function of a first signal and a second signal and outputting the expected vehicle deceleration value to a shift decision control unit for implementing a transmission gear shift. The first signal is indicative of an engine torque and the second signal is indicative of an input shaft rotational speed. The first signal may be measured at the transmission output shaft or may be provided by an engine control module. The second signal may also be measured at the transmission output shaft.
The expected vehicle deceleration during the transmission gear shift may be calculated using the torque on the transmission due to vehicle drag forces, gross vehicle weight, and a constant. The constant may be a function of the axle ratio of the vehicle and the radius of a tire disposed on the vehicle.
According to another aspect of the invention, the method may comprise the steps of providing a set of initial values for a current time period, determining a set of estimated values for a future time period, providing an estimated vehicle deceleration value to a shift decision control unit, calculating a set of error values, calculating a set of correction values, and adjusting the set of estimated values using the set of correction values.
The set of initial values may include an engine torque value, an input shaft rotational speed value, and a vehicle deceleration value. The set of estimated values for a future time period may include an estimated engine torque value, an estimated input shaft rotational speed rotational value, and an estimated vehicle deceleration value. The step of providing the engine vehicle deceleration value to a shift decision control unit may be performed after adjusting the set of estimated values using the set of correctional values.
The set of error values may be based on the first signal, the second signal, and a subset of the set of estimated values. The subset of the set of estimated values may comprise the estimated engine torque value and the estimated input shaft rotational speed value. The set of estimated values may be used as the set of initial values in a future time period. The set of correction values may be calculated using the set of error values and a set of predetermined coefficients.